Antarctica's ice-sheet melt could reshape global coastlines

Researchers combining nine models estimate Antarctic ice shelves have lost about 843 billion tonnes a year from melting underneath in recent decades, and scientists say the ice sheets will continue losing mass while the pace and total future loss remain uncertain.

Scientists are working to understand how fast Antarctic ice shelves are melting from below and why that matters for coastlines worldwide. A recent synthesis brought together modelling on basal melt from nine groups to improve estimates. The analysis finds that, over recent decades, Antarctic ice shelves lost about 843 billion tonnes of mass per year from melting at their undersides. Researchers say the ice sheets will keep losing mass, but there is large uncertainty about how fast and how much they will change. Key findings: - Nine modelling groups estimate Antarctic ice shelves lost roughly 843 billion tonnes per year from basal melting in recent decades. - Ice shelves float on the ocean and do not raise sea level directly when they melt, but their weakening can allow grounded ice to flow faster into the ocean, contributing to future sea level rise. - Some Antarctic regions contain enough ice to raise global sea levels by about 15 metres if fully lost, and individual catchments such as Denman hold amounts equivalent to about 1.5 metres of global sea level rise. - Data on conditions beneath ice shelves are limited, which contributes to substantial uncertainty in projections. Summary: The modelling synthesis refines estimates of ocean-driven mass loss from Antarctic ice shelves but leaves important uncertainties about timing and magnitude of future sea level rise. Researchers intend to use these results to improve projections, and international scientific effort continues to address gaps in under-ice observations.